This invention relates generally to the field of petroleum hydrocarbon production, recovery and handling. More specifically, this invention relates to an improved system and method for fluidizing, separating, and recovering highly viscous residual petroleum products such as sludge and the like which can adhere to inorganic surfaces such as process equipment including pumps, valves, and flow conduits and the like, as well as contaminant solids such as sand or clay and the like. The invention mechanically and chemically separates the residual petroleum products from the associated inorganic material to facilitate processing, to recover otherwise waste or unusable petroleum products, and to clean contaminant solids such as sand or clay in a manner accommodating environmentally compatible re-use or disposal.
In the petroleum industry, subterranean oil deposits are identified and tapped by means of one or more extraction pumps designed to draw flowable crude oil to the surface for subsequent transport by means of pipelines and/or ocean-going tanker vessels and the like to a refinery, whereat the extracted crude oil is processed to produce a wide range of different specific petroleum products and by-products. The petroleum industry, however, is plagued by a number of important problems and limitations, some of which pose significant environmental and worker safety hazards.
More particularly, as crude oil is extracted from a subterranean deposit over a period of time, the subterranean strata particularly in the region close to the extraction pump or well-head gradually becomes clogged or plugged with a highly viscous hydrocarbon-based sludge that is typically mixed with inorganic material such as sand and clay particles and the like. This sludge material effectively reduces the flow of less viscous and recoverable crude oil to the well-head, thereby significantly reducing the crude oil production rate from the subterranean deposit. In some instances, production from an operational but sludge-clogged well-head can become uneconomical with as much as 85% of the oil deposit remaining in the ground, resulting in abandonment of the operational well-head, and, in some cases, costly drilling and installation of a replacement well-head at a different location to resume oil field production.
This viscous hydrocarbon sludge material also contacts and adheres to surfaces of process equipment such as pump, valves, and flow conduits within the well-head and any associated pipeline of other tanks and the like used to transport the crude oil from the oil field to the refinery. Once again, over time, these sludge coatings build up and clog these process equipment surfaces, resulting in reduced pumping and related flow rates. Periodic cleaning of accumulated sludge coatings from process equipment surfaces has been difficult, and normally involves the use of and exposure of workmen to toxic materials and dangerous working conditions, sometimes with minimal cleaning effectiveness. In addition, the accumulated sludge deposits cleaned from such process equipment surfaces, together with solvent-based cleaning solutions, comprise toxic wastes, which are subject to costly handling and disposal.
In addition to the foregoing, the extracted crude oil commonly includes a certain percentage of suspended solid contaminants particularly such as inorganic sand or clay particles having hydrocarbon molecules adhered thereto. To avoid negative economic value attributable to the presence of these contaminants, settling tanks or ponds are often employed to allow at least some of the solid contaminants to settle to the bottom before the remaining crude oil is skimmed off for refining. The resultant sediment comprises a highly thick and viscous, almost solid petroleum-based sludge consisting of the solid contaminants such as sand or clay particles, which are coated with hydrocarbon molecules adhered thereto. This tank sludge is very difficult to fluidize and remove from the bottom of a settling tank or pond, and, once again, requires exposure of workmen to toxic materials and dangerous working conditions, and further represents a highly toxic waste product.
The above-described petroleum sludge products typically include heavy organic molecules such as paraffin/wax, resin, asphaltene, diamonoid, mercaptans, and organometallic compounds. As noted above, such organic compounds can be carried with the crude oil and precipitate out at various stages of the petroleum production process, resulting in sludge accumulation within tanks and/or blockages within pumps, valves, pipelines, and other handling and processing equipment. Various intermolecular and interparticle forces are responsible for such precipitation and deposition, and the deposited particles can stick or adhere to the wall of almost any equipment contacted therewith. The toughness of the precipitate and its behavior depend largely upon the presence of asphaltene and/or paraffin/wax in the crude oil. Asphaltene, which is a highly polar compound that is insoluble in aliphatic hydrocarbons from crude oil, is present in the form of relatively stable colloidal particles. When destabilized during production or processing, asphaltene can deposit onto contacted surfaces as a “glue and mortar” type precipitate, resulting in hardening other components of the crude oil to form extremely viscous and virtually solid sludge deposits. When such deposits are combined with highly polar solid contaminants such as sand and clay particles, the virtually solid character of the sludge deposit is enhanced.
Wax present in crude oil forms deposits due to different reasons. Petroleum wax consists primarily of linear paraffin hydrocarbons (C18-C36) and naphtenic hydrocarbons (C30-C60), and such hydrocarbons of wax can exist in either liquid amorphous pumpable state or solid crystalline form. Wax/paraffin may deposit due to lowering of crude oil temperature and phase transformation from liquid amorphous into crystalline solid form. Wax crystallization is influenced by the presence of asphaltene and sand. Such complex mixtures often form deposits that cannot be re-fluidized by simple reheating of the system or by the introduction of aromatic solvents.
Accordingly, heretofore, a satisfactory integrated, economical, effective and efficient, and relatively environmentally compatible system and method have not existed for dealing with these petroleum-based sludge problems. Instead, current systems and methods have relied upon a variety of chemical and mechanical methods which expose workers to very toxic and dangerous conditions and chemicals, and often significantly increase the amount of a waste stream that contains hazardous materials and is thus subject to complex and costly disposal methods. In addition, current solvent-based chemical compositions used to remove and/or clean heavy oil, oils from tar sands, and residual down-hole sludge in a well are often very expensive yet offer minimal if any success.
There exists, therefore, a significant need for improvements in and to systems and methods for recovering heavy and/or viscous petroleum, for fluidizing petroleum-based sludge formations, for cleaning accumulated sludge and tar formations from surfaces of petroleum processing equipment, and for separating petroleum hydrocarbon molecules from solid contaminants such as sand and clay, all to permit and facilitate substantially optimized petroleum recovery and to provide a substantially clean solids by-product which can be disposed or subjected to alternative uses in an environmentally safe and friendly manner. The present invention fulfills all of these needs, and provides further related advantages.